While those of us here in the early 21st century argue over the future of smartwatches and smart rings, inventors of the 1920s would probably think we're all a bunch of babies. Sure, your Pebble might have caller ID. But can it incapacitate a potential mugger with a 10,000 volt high frequency shock? I didn't think so.

Smartwatch? Please. We've already moved on to smart rings, magical digit-wrappers that control …
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In 1927, the shockwatch was the future of fighting off bad guys. At least it was supposed to be, if they could only figure out a way to get the batteries smaller.

Inventor Emil Pruss, proudly pictured above with his "electric wristlet,' insisted that not only was it effective for personal protection, it was completely harmless to the wearer. Y'know, because of the wrist strap's insulation.

There were a couple of different designs, but both were dependent on enormous batteries. See that huge black box in Emil's left hand? Not exactly the most convenient set-up for someone just going about their day, let alone fending off an attacker.

From the March 1927 issue of Science and Invention magazine:

The device is very compact, being about the same size and the same shape as a wrist watch, and it produces a current sufficient to cause a sever shock. Such a current may be produced by either of the two methods illustrated in the accompanying diagrams. The use of the spark coil is perhaps a simpler method, but a higher potential will be obtained by the use of a high frequency coil.

Obviously, this idea was way ahead of its time. And much like the problems we face today for countless gadget ideas, this shockwatch couldn't be miniaturized properly due to the relatively primitive battery technology of the era.

Today, the most basic stun guns can deliver 400,000 volts off of a lone 9 volt battery. And our smartphones can even be armed with 650,000-volt stunners like the Yellow Jacket iPhone attachment. Just be sure to turn on the safety before making a call.